Deep Trench Charge Storage Cell With Diffusion-Formed Doped Region
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Solution Overview
Problem
Current manufacturing techniques for vertical storage photodiodes in image sensors limit charge storage capacity due to high-energy ion implantation, which increases lattice defects and dark current, and are hindered by thick photoresist layers, restricting the depth of dopant penetration and thus the storage volume.
Innovation Solution
The method involves creating trenches in a semiconductor substrate, filling one trench with a doped material and another with undoped material, annealing to diffuse the dopant, and filling the trenches with polysilicon for capacitive deep trench isolation, thereby forming doped regions for charge storage without the need for high-energy ion implantation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high-energy ion implantation is used to increase dopant penetration depth, then charge storage capacity is improved, but lattice defects and dark current increase
Solution Approach 1:
The patent replaces the mechanical ion implantation process with a chemical diffusion process. Instead of using high-energy ion bombardment to introduce dopants, the invention uses thermal diffusion where dopant atoms naturally diffuse into the semiconductor substrate through concentration gradients during annealing, thereby achieving deep dopant penetration without creating lattice defects
Solution Approach 2:
The patent changes the fundamental parameter of dopant introduction from high-energy physical implantation to low-energy thermal diffusion. By controlling temperature and time parameters during the annealing process, the invention achieves controlled dopant penetration depth without the harmful effects of high-energy ion implantation
2Quantity of substance
If thick photoresist layers are used to enable deeper dopant penetration, then charge storage volume is improved, but manufacturing complexity increases
Solution Approach 1:
The patent performs preliminary trench formation and dopant placement before the diffusion process. By pre-defining the trench structures and filling them with dopant-containing materials, the invention eliminates the need for thick photoresist layers to control dopant depth, as the trench depth itself defines the diffusion path
Solution Approach 2:
The patent introduces trenches as intermediary structures that facilitate controlled dopant diffusion. These trenches act as channels that guide dopant atoms to specific depths in the substrate, replacing the need for thick photoresist layers as depth-control intermediaries
3Quantity of substance
If dopant penetration depth is increased to enhance storage capacity, then charge storage capacity is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent pre-forms trenches to specific depths before introducing dopants. This preliminary structuring defines the maximum diffusion path length, thereby controlling dopant penetration depth without requiring precise control of the diffusion process itself, reducing manufacturing precision requirements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances charge storage capacity by increasing dopant penetration depth without lattice defects, improving the balance between memory and photodiode storage, and allows for a more efficient global shutter imaging device.
Implementation Method 1
annealing the substrate material to cause said one dopant to diffuse from said first trench and to thereby provide a doped region adjacent said first trench
Data Source
Figure 1
Figure 2a~2b
Figure 2c~2d
AI summary
A method of manufacturing a charge storage memory cell comprises providing a first trench and a second trench in a substrate material. The first trench is filled with a doped material comprising one of a P dopant and an N dopant. The second trench is filled with a second trench material. The method comprises causing the one dopant to diffuse from the first trench to thereby provide a doped region adjacent to the first trench. The material from the first and second trenches us removed and at least one of the trenches is filled with a capacitive deep trench isolation material to provide capacitive deep trench isolation.